The disclosure relates to aluminum alloys. More particularly, the disclosure relates to aluminum alloys containing an icosahedral phase (I-phase) for use in aerospace applications.
Since the discovery of the existence of an icosahedral phase (I-phase) in 1984, a number of documents discuss the composition and mechanical properties of aluminum alloys containing such a phase. Examples include U.S. Pat. No. 4,772,370 and US Patent Application Publication 2010/0003536A1. More recently, the idea of using I-phase materials for coatings has also surfaced. While many references assert that aluminum alloys with the I-phase have high ductility, these measurements are usually based on bending and such a mode of stress does not, in general, coincide with the ability of a material to deform in pure tension. Tests in pure tension have shown that I-phase materials behave poorly, often exhibiting tensile failures near 1% elongation. This behavior has often been attributed to the high volume fractions (e.g., as high as 80%, see U.S. Pat. No. 6,334,911) of I-phase produced in alloys explored to date. However, a variety of other factors can be involved; that is, hydrogen content, phases that have a low volume fraction, but embrittle aluminum alloys, or the size and distribution of I-phase particles, even at low volume fractions.
It has been documented that transition metal elements such as Co can be added to ternary aluminum I-phase alloys, such as Al—Cr—Co or Al—Mn—Co, and this results in a finer size and distribution of I-phase particles. See, K. Kita, K. Saitoh, A. Inoue, T. Masumoto, “Mechanical Properties of Al Based Alloys Containing Quasi-crystalline Phase as a Main Component”, Materials Science and Engineering, A226-228, 1997, pp. 1004-1007 (hereafter “Kita et al.”). Kita et al. assert that this results in greater strength, although it is not clear that some strength is not derived from the compound Al9Co2.